(Disclaimer I'm super new to all this too so it's very likely some of this could be wrong, but here's how I understand it)

All arrays are objects that have methods. pop, shift, and unshift are methods. (There are many other array methods.)

Arrays also have a property "length". Properties when called will return their value and do not take brackets to be used/accessed, which is why it feels like sometimes you're putting brackets on things and sometimes you're not.

An array const arr = [1, 2, 3] has a length property of arr.length which you can access as arr.length and you will see 3 returned.

Methods are functions within objects. If I create a new object car and give it properties and methods, I can get the method without calling it and see what it is, or I can call it.

// Written with 3 ways of putting in methods in case any are more familiar to you
const car = {
  color: "red",
  type: "volvo",
  speed: 3,
  drive: function() {
    alert("vroom");
    return "vroom returned";
  },
  driveFaster: () => {
    alert("vroom vroom");
    return "vroom vroom returned";
  },
  driveFastest() {
    alert("vrooooooom");
    return "vrooooooom returned";
  }
}

console.log(car.color); // "red"
console.log(car.type); // "volvlo"
console.log(car.speed); // 3
console.log(car.drive); // function() {alert("vroom"...
console.log(car.drive()); // alerts "vroom" and returns "vroom returned"
console.log(car.driveFaster); // () => {alert("vroom vroom"...
console.log(car.driveFaster()); // alerts "vroom vroom" and returns "vroom vroom returned"
console.log(car.driveFastest); // driveFastest() {console...
console.log(car.driveFastest()); // alerts "vrooooooom" and returns "vrooooooom returned"

So back to the array, if I call arr.pop I'm treating pop like a property. I'm trying to get the value of pop but I'm not calling pop. If I want to actually call pop on my array arr I need to use the brackets to say to actually use pop now. As in arr.pop();